Refrigeration cycle apparatus

ABSTRACT

In a refrigeration cycle apparatus according to the present disclosure, the circulation direction of refrigerant is switched between a first circulation direction and a second circulation direction opposite to the first circulation direction. The first circulation direction is a circulation direction in order of a compressor, a first heat exchanger, a first expansion valve, a third heat exchanger, a fourth heat exchanger, a second expansion valve, and a second heat exchanger. When a circulation direction of the refrigerant is the first circulation direction, the refrigerant from the third heat exchanger exchanges heat with the refrigerant from the second heat exchanger in the fourth heat exchanger. When a circulation direction of the refrigerant is the second circulation direction, the refrigerant from the fourth heat exchanger exchanges heat with the refrigerant from the first heat exchanger in the third heat exchanger.

TECHNICAL FIELD

The present disclosure relates to a refrigeration cycle apparatus in which the circulation direction of refrigerant is switched between a first circulation direction and a second circulation direction opposite to the first circulation direction.

BACKGROUND ART

A refrigeration cycle apparatus in which the circulation direction of refrigerant is switched between a first circulation direction and a second circulation direction opposite to the first circulation direction has been known. For example, Japanese Patent No. 6058145 (PTL 1) discloses an air conditioning apparatus in which an indoor unit includes an expansion valve and an outdoor unit includes an expansion valve, and these two expansion valves are connected to each other via an extension pipe. In the air conditioning apparatus during a heating operation, the expansion valve of the indoor unit reduces the pressure of refrigerant to turn the refrigerant into a gas-liquid two-phase state, and the refrigerant in the gas-liquid two-phase state flows through the extension pipe. In the air conditioning apparatus during a cooling operation, the expansion valve of the outdoor unit reduces the pressure of refrigerant to turn the refrigerant into a gas-liquid two-phase state, and the refrigerant in the gas-liquid two-phase state flows through the extension pipe. Namely, in the air conditioning apparatus, the refrigerant in the gas-liquid two-phase state (wet steam) flows through the extension pipe during both the heating operation and the cooling operation. Because the density of the wet steam is lower than the density of refrigerant in the liquid state (liquid refrigerant), the amount of refrigerant circulating through the air conditioning apparatus can be reduced.

CITATION LIST Patent Literature

-   PTL 1: Japanese Patent No. 6058145

SUMMARY OF INVENTION Technical Problem

In the air conditioning apparatus disclosed in PTL 1, liquid refrigerant flows into one expansion valve, the expansion valve reduces the pressure of the refrigerant to turn the refrigerant into wet steam, and the wet steam flows into the other expansion valve, during both the heating operation and the cooling operation. For a refrigeration cycle apparatus in which the circulation direction of refrigerant can be switched like the above-identified air conditioning apparatus, it has to be assumed that both liquid refrigerant and wet steam may flow into each of the two expansion valves.

When it is necessary to ensure a certain refrigerant flow rate while keeping a pressure difference between refrigerant flowing into an expansion valve and the refrigerant flowing out of the expansion valve, the lower the density of refrigerant flowing into the expansion valve, the higher the flow coefficient (Cv value) of the expansion valve should be. Thus, the maximum value of the Cv value of an expansion valve into which wet steam is to flow should be larger than the maximum value of the Cv value of an expansion valve into which only liquid refrigerant is to flow.

When it is assumed that both liquid refrigerant and wet steam may flow into an expansion value, there is a large difference between the minimum value of the Cv value and the maximum value of the Cv value, resulting in a large variation (resolution) of the Cv value corresponding to the minimum value of the operational amount for the opening degree of the expansion valve. In other words, the controllability for the expansion valve is deteriorated to cause an increase of the difference between the actual refrigerant flow rate and a desired refrigerant flow rate. Because the capacity of the refrigeration cycle apparatus is regulated through regulation of the refrigerant flow rate, the deteriorated controllability for the expansion valve causes deterioration of the controllability for the refrigeration cycle apparatus.

The present disclosure has been made to solve the problems as described above, and its object is to suppress deterioration of the controllability for the refrigeration cycle apparatus.

Solution to Problem

In a refrigeration cycle apparatus according to the present disclosure, a circulation direction of refrigerant is switched between a first circulation direction and a second circulation direction opposite to the first circulation direction. The refrigeration cycle apparatus includes: a compressor; a first heat exchanger; a second heat exchanger; a third heat exchanger; a fourth heat exchanger; a first expansion valve; and a second expansion valve. The first circulation direction is a circulation direction in order of the compressor, the first heat exchanger, the first expansion valve, the third heat exchanger, the fourth heat exchanger, the second expansion valve, and the second heat exchanger. When a circulation direction of the refrigerant is the first circulation direction, the refrigerant from the third heat exchanger exchanges heat with the refrigerant from the second heat exchanger in the fourth heat exchanger. When a circulation direction of the refrigerant is the second circulation direction, the refrigerant from the fourth heat exchanger exchanges heat with the refrigerant from the first heat exchanger in the third heat exchanger.

Advantageous Effects of Invention

In the refrigeration cycle apparatus according to the present disclosure, when a circulation direction of the refrigerant is the first circulation direction, the refrigerant from the third heat exchanger exchanges heat, in the fourth heat exchanger, with the refrigerant from the second heat exchanger and, when a circulation direction of the refrigerant is the second circulation direction, the refrigerant from the fourth heat exchanger exchanges heat, in the third heat exchanger, with the refrigerant from the first heat exchanger. Accordingly, deterioration of the controllability can be suppressed.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a functional configuration of an air conditioner that is an example of a refrigeration cycle apparatus according to Embodiment 1, together with flow of refrigerant during a cooling operation.

FIG. 2 shows the functional configuration of the air conditioner in FIG. 1, together with flow of refrigerant during a heating operation.

FIG. 3 is a functional block diagram showing a configuration of a controller in FIGS. 1 and 2.

FIG. 4 shows a functional configuration of an air conditioner according to a comparative example, together with flow of refrigerant during a cooling operation.

FIG. 5 shows the functional configuration of the air conditioner in FIG. 4, together with flow of refrigerant during a heating operation.

FIG. 6 shows an example of an internal structure of an expansion valve 5 used in the air conditioner in FIGS. 1 and 2 and the air conditioner in FIGS. 4 and 5.

FIG. 7 is an enlarged view of a leading end and a valve seat and therearound of the expansion valve in FIG. 6.

FIG. 8 shows a relation between the opening degree and the Cv value of an expansion valve.

FIG. 9 is a P-h diagram showing change of the state of refrigerant circulating through the air conditioner in FIG. 1.

FIG. 10 is a P-h diagram showing change of the state of refrigerant circulating through the air conditioner in FIG. 2.

FIG. 11 shows a functional configuration of an air conditioner that is an example of a refrigeration cycle apparatus according to Embodiment 2, together with flow of refrigerant during a cooling operation.

FIG. 12 shows the functional configuration of the air conditioner in FIG. 11, together with flow of refrigerant during a heating operation.

FIG. 13 shows a functional configuration of an air conditioner that is an example of a refrigeration cycle apparatus according to a modification of Embodiment 2, together with flow of refrigerant during a cooling operation.

FIG. 14 shows the functional configuration of the air conditioner in FIG. 13, together with flow of refrigerant during a heating operation.

DESCRIPTION OF EMBODIMENTS

In the following, embodiments of the present disclosure are described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference characters, and the description thereof is not repeated in general.

Embodiment 1

FIG. 1 shows a functional configuration of an air conditioner 100 that is an example of a refrigeration cycle apparatus according to Embodiment 1, together with flow of refrigerant during a cooling operation. As shown in FIG. 1, air conditioner 100 includes an outdoor unit 110 and an indoor unit 120. Outdoor unit 110 and indoor unit 120 are connected to each other by each of extension pipes ep1 and ep2. Air conditioner 100 performs air conditioning for an indoor space where indoor unit 120 is placed.

Outdoor unit 110 includes a compressor 1, a four-way valve 2, a switch 3 (first switch), a heat exchanger 4 (first heat exchanger), an expansion valve 5A (first expansion valve), an internal heat exchanger 6 (third heat exchanger), and a controller 10. Indoor unit 120 includes an internal heat exchanger 7 (fourth heat exchanger), an expansion valve 5B (second expansion valve), a heat exchanger 8 (second heat exchanger), and a switch 9 (second switch). Expansion valves 5A and 5B have respective structures similar to each other. Controller 10 may alternatively be included in indoor unit 120, or placed separately from outdoor unit 110 and indoor unit 120.

During a cooling operation, refrigerant circulates in a circulation direction (first circulation direction) in order of compressor 1, four-way valve 2, heat exchanger 4, expansion valve 5A, internal heat exchanger 6, internal heat exchanger 7, expansion valve 5B, heat exchanger 8, and four-way valve 2. Refrigerant flowing out of outdoor unit 110 flows into indoor unit 120 through extension pipe ep1. Refrigerant flowing out of indoor unit 120 flows into outdoor unit 110 through extension pipe ep2. During the cooling operation, heat exchanger 4 serves as a condenser and heat exchanger 8 serves as an evaporator.

Switch 3 includes a check valve 31 (first check valve) and a check valve 32 (second check valve). Internal heat exchanger 6 is connected between an output port of check valve 31 and an input port of check valve 32. The output port of check valve 31 is connected to heat exchanger 4. During the cooling operation, an input port of check valve 31 communicates with a discharge port of compressor 1 through four-way valve 2. Refrigerant from four-way valve 2 flows through check valve 31 toward heat exchanger 4 without flowing through check valve 32. Namely, switch 3 directs refrigerant from compressor 1 to flow to heat exchanger 4 without flowing through internal heat exchanger 6. The pressure of refrigerant flowing out of check valve 31 is lower than the pressure of refrigerant flowing into check valve 31, because of a pressure loss due to check valve 31. Most of the refrigerant from check valve 31 therefore flows toward heat exchanger 4.

Switch 9 includes a check valve 91 (third check valve) and a check valve 92 (fourth check valve). Internal heat exchanger 7 is connected between an input port of check valve 91 and an output port of check valve 92. An output port of check valve 91 is connected to heat exchanger 8 and an input port of check valve 92. During the cooling operation, refrigerant from heat exchanger 8 flows through check valve 92 toward heat exchanger 7 without flowing through check valve 91. Namely, switch 9 directs the refrigerant from heat exchanger 8 to flow through internal heat exchanger 7 to compressor 1. In internal heat exchanger 7, heat is exchanged between refrigerant from internal heat exchanger 6 and refrigerant from heat exchanger 8. The pressure of refrigerant flowing out of internal heat exchanger 7 is lower than the pressure of refrigerant flowing into check valve 92 because of a pressure loss due to check valve 92 and internal heat exchanger 7. Most of the refrigerant from internal heat exchanger 7 therefore flows toward four-way valve 2.

During the cooling operation, a node N1 is a node through which refrigerant flowing from four-way valve 2 to compressor 1 passes. A node N2 is a node through which refrigerant flowing from compressor 1 to check valve 31 passes. A node N3 is a node through which refrigerant flowing from check valve 31 to heat exchanger 4 passes. A node N4 is a node through which refrigerant flowing from heat exchanger 4 to expansion valve 5A passes. A node N5 is a node through which refrigerant flowing from expansion valve 5A to internal heat exchanger 6 passes. A node N6 is a node through which refrigerant flowing from internal heat exchanger 6 to extension pipe ep1 passes. A node N7 is a node through which refrigerant flowing from extension pipe ep1 to internal heat exchanger 7 passes. A node N8 is a node through which refrigerant flowing from internal heat exchanger 7 to expansion valve 5B passes. A node N9 is a node through which refrigerant flowing from expansion valve 5B to heat exchanger 8 passes. A node N10 is a node through which refrigerant flowing from heat exchanger 8 to internal heat exchanger 7 passes. A node N11 is a node through which refrigerant flowing from internal heat exchanger 7 to extension pipe ep2 passes. A node N12 is a node through which refrigerant flowing from extension pipe ep2 to four-way valve 2 passes.

Controller 10 controls the driving frequency of compressor 1 so as to control the amount of refrigerant discharged from compressor 1 per unit time, so that the temperature of the indoor space reaches a target temperature (set by a user, for example). Controller 10 controls the opening degree of expansion valve 5A and the opening degree of expansion valve 5B so that the pressure difference between refrigerant after being discharged from compressor 1 and before being reduced in pressure and the refrigerant after being reduced in pressure and before being sucked into compressor 1 has a value within a desired range. Expansion valve 5A and expansion valve 5B may be controlled so that the degree of superheat of refrigerant and the degree of supercooling of refrigerant each have a target value. Controller 10 controls four-way valve 2 to switch the circulation direction of refrigerant between the circulation direction for the cooling operation and the circulation direction for the heating operation.

FIG. 2 shows the functional configuration of air conditioner 100 in FIG. 1, together with flow of refrigerant during a heating operation. As shown in FIG. 2, during a heating operation, refrigerant circulates in a circulation direction (second circulation direction) in order of compressor 1, four-way valve 2, heat exchanger 8, expansion valve 5B, internal heat exchanger 7, internal heat exchanger 6, expansion valve 5A, heat exchanger 4, and four-way valve 2. Refrigerant flowing out of outdoor unit 110 flows into indoor unit 120 through extension pipe ep2. Refrigerant flowing out of indoor unit 120 flows into outdoor unit 110 through extension pipe ep1. During the heating operation, heat exchanger 8 serves as a condenser and heat exchanger 4 serves as an evaporator.

During the heating operation, the input port of check valve 31 communicates with a suction port of compressor 1 through four-way valve 2. Refrigerant from four-way valve 2 flows through check valve 91 toward heat exchanger 8 without flowing through internal heat exchanger 7. Namely, switch 9 directs refrigerant from compressor 1 to flow to heat exchanger 8 without flowing through internal heat exchanger 7. The pressure of refrigerant flowing out of check valve 91 is lower than the pressure of refrigerant flowing into check valve 91 because of a pressure loss due to check valve 91. Most of the refrigerant from check valve 91 therefore flows toward heat exchanger 8.

Refrigerant from heat exchanger 4 flows through internal heat exchanger 6 and check valve 32 in this order toward four-way valve 2, without flowing through check valve 31. Namely, switch 3 directs refrigerant from heat exchanger 4 to flow through internal heat exchanger 6 to compressor 1. In internal heat exchanger 6, heat is exchanged between refrigerant from internal heat exchanger 7 and refrigerant from heat exchanger 4. The pressure of refrigerant flowing out of check valve 32 is lower than the pressure of refrigerant flowing into internal heat exchanger 6 because of a pressure loss due to internal heat exchanger 6 and check valve 32. Most of refrigerant from check valve 32 therefore flows toward four-way valve 2.

During the heating operation, node N1 is a node through which refrigerant flowing from four-way valve 2 to compressor 1 passes. Node N12 is a node through which refrigerant flowing from four-way valve 2 to extension pipe ep2 passes. Node

N11 is a node through which refrigerant flowing from extension pipe ep2 to check valve 91 passes. Node N10 is a node through which refrigerant flowing from check valve 91 to heat exchanger 8 passes. Node N9 is a node through which refrigerant flowing from heat exchanger 8 to expansion valve 5B passes. Node N8 is a node through which refrigerant flowing from expansion valve 5B to internal heat exchanger 7 passes. Node N7 is a node through which refrigerant flowing from internal heat exchanger 7 to extension pipe ep1 passes. Node N6 is a node through which refrigerant flowing from extension pipe ep1 to internal heat exchanger 6 passes. Node N5 is a node through which refrigerant flowing from internal heat exchanger 6 to expansion valve 5A passes. Node N4 is a node through which refrigerant flowing from expansion valve 5A to heat exchanger 4 passes. Node N3 is a node through which refrigerant flowing from heat exchanger 4 to internal heat exchanger 6 passes. Node N2 is a node through which refrigerant flowing from internal heat exchanger 6 to four-way valve 2 passes.

FIG. 3 is a functional block diagram showing a configuration of controller 10 in FIGS. 1 and 2. As shown in FIG. 3, controller 10 includes circuitry 11, a memory 12, and an input/output unit 13. Circuitry 11 may be dedicated hardware, or a CPU (Central Processing Unit) executing a program stored in memory 12. When circuitry 11 is dedicated hardware, circuitry 11 is, for example, a single circuit, a composite circuit, a programmed processor, a parallel-programmed processor, an ASIC (Application Specific Integrated Circuit), an FGA (Field Programmable Gate Array), or a combination thereof. When circuitry 11 is a CPU, the functions of controller 10 are implemented by software, firmware, or a combination of software and firmware. The software or firmware is written as a program and stored in memory 12. Circuitry 11 reads and executes the program stored in the memory. Memory 12 includes a non-volatile or volatile semiconductor memory (for example, RAM (Random Access Memory), ROM (Read Only Memory), flash memory, EPROM (Erasable Programmable Read Only Memory), or EEPROM (Electrically Erasable Programmable Read Only Memory)), a magnetic disc, a flexible disc, an optical disc, a compact disc, a mini disc, or a DVD (Digital Versatile Disc). The CPU is also called central processing unit, processing unit, arithmetic unit, microprocessor, microcomputer, processor, or DSP (Digital Signal Processor).

FIG. 4 shows a functional configuration of an air conditioner 900 according to a comparative example, together with flow of refrigerant during a cooling operation. FIG. 5 shows the functional configuration of air conditioner 900 in FIG. 4, together with flow of refrigerant during a heating operation. The configuration of air conditioner 900 corresponds to the configuration of air conditioner 100 shown in FIGS. 1 and 2, except that internal heat exchangers 6, 7 and switches 3, 9 of air conditioner 100 are not present and expansion valves 5A, 5B of air conditioner 100 are replaced with expansion valves 5C, 5D, respectively. Expansion valves 5C and 5D have respective structures similar to each other. The configuration of air conditioner 900 and the configuration of air conditioner 100 are similar to each other except for the above-identified features, and therefore, the description thereof is not herein repeated.

As shown in FIGS. 4 and 5, the circulation direction of refrigerant in air conditioner 900 is switched between a direction for the cooling operation and a direction for the heating operation. With reference to FIG. 4, during the cooling operation, liquid refrigerant flows into expansion valve 5C and wet steam flows into expansion valve 5D. With reference to FIG. 5, during the heating operation, liquid refrigerant flows into expansion valve 5D and wet steam flows into expansion valve 5C. It has to be assumed that both liquid refrigerant and wet steam may flow into each of expansion valves 5C, 5D in air conditioner 900.

FIG. 6 shows an example of an internal structure of expansion valve 5 used in air conditioner 100 in FIGS. 1 and 2 and air conditioner 900 in FIGS. 4 and 5. As shown in FIG. 6, expansion valve 5 includes a main body 51, a valve body 52, a stepper motor 53, and coupling pipes 54, 55. In main body 51, valve chambers 511, 512 are formed, and these valve chambers communicate with each other through a valve seat 513 that is a hole through which refrigerant flows. Valve seat 513 is a cylindrical hole, for example. Coupling pipe 54 is connected to main body 51 so as to allow the outside and valve chamber 511 to communicate with each other. Coupling pipe 55 is connected to main body 51 so as to allow the outside and valve chamber 512 to communicate with each other.

Valve body 52 is disposed to extend from stepper motor 53 toward valve seat 513 through valve chamber 511. Valve body 52 has a leading end 521 in an acute shape which is, for example, a conical shape. The diameter of valve body 52 is substantially identical to the diameter of valve seat 513. Valve body 52 is moved by stepper motor 53 in the directions indicated by an arrow M1 and its position is determined. The position of valve body 52 determines the ratio of leading end 521 occupying valve seat 513 to the whole valve seat 513. Namely, stepper motor 53 determines the opening degree of expansion valve 5 to regulate the flow rate through valve seat 513 per unit time and regulate the pressure reduction by expansion valve 5.

Generally, it is often the case that an expansion valve for a refrigeration cycle apparatus is selected by determining the Cv value based on the specifications of a fluid for the refrigeration cycle apparatus and comparing the Cv value with Cv values presented by valve manufactures so as to determine the valve type and the diameter of the valve seat of the expansion valve. Comparison of the Cv values is one of convenient ways used for selecting an expansion valve.

The Cv value is defined as “a numerical value (dimensionless) expressed in US gal/min (1 US gal=3.785 L) of the flow rate of water at a temperature of 60° F. (about 15.5° C.) that will flow through a valve (expansion valve) with a specific opening degree and a pressure difference of 1 lb/in² [6.895 kPa]. The Cv value is expressed by the following expression (1).

[Expression  1]                                     $\begin{matrix} {{Cv} = {\alpha \cdot {Gr} \cdot \sqrt{\frac{1}{\Delta\;{P \cdot \rho}}}}} & (1) \end{matrix}$

In the expression (1), α is a constant, Gr is the refrigerant flow rate [kg/s], ΔP is the pressure difference [MPa] between refrigerant flowing into the expansion valve and the refrigerant flowing out of the expansion valve, and ρ is the density [kg/m³] of the refrigerant flowing into the expansion valve. When it is necessary to ensure a certain refrigerant flow rate Gr while keeping the pressure difference ΔP, the lower the density of refrigerant flowing into the expansion valve, the higher Cv value of the expansion valve should be, as seen from the expression (1). It is therefore necessary that the maximum value of the Cv value of an expansion value into which wet steam flows should be higher than the maximum value of the Cv value of an expansion valve into which only liquid refrigerant flows.

FIG. 7 is an enlarged view of leading end 521 and valve seat 513 and therearound of expansion valve 5 in FIG. 6. Leading end 521 shown in FIG. 7 (b) has a diameter D2 larger than a diameter D1 of leading end 521 shown in FIG. 7 (a). The larger the diameter of leading end 521, the larger the maximum value of the Cv value of expansion valve 5, and therefore, a maximum value Cv2 of the Cv value of expansion valve 5 shown in FIG. 7 (b) is larger than a maximum value Cv1 of the Cv value of expansion valve 5 shown in FIG. 7 (a). Expansion valve 5 shown in FIG. 7 (a) and expansion valve 5 shown in FIG. 7 (b) have the same height H1 of leading end 521 and also have the same minimum value Cv0 of the Cv value.

FIG. 8 shows a relation between the opening degree and the Cv value of an expansion valve. In FIG. 8, a relation R1 represents a relation between the opening degree and the Cv value of expansion valve 5 in FIG. 7 (a). A relation R2 represents a relation between the opening degree and the Cv value of expansion valve 5 in FIG. 7 (b). The relation between the opening degree and the Cv value of an expansion valve is represented by a monotonous increase, for example, and FIG. 8 shows a case where each of Relations R1 and R2 is a linear relation. An opening degree Omin is the minimum opening degree of expansion valve 5, and an opening degree Omax is the maximum opening degree of expansion valve 5. An opening degree difference Od is an opening degree difference corresponding to the minimum operational amount of the stepper motor of expansion valve 5.

As shown in FIG. 8, the slope of the straight line representing relation R2 is larger than the slope of the straight line representing relation R1. Accordingly, with regard to the variation (resolution) of the Cv value corresponding to the opening degree difference Od, a resolution Rs2 of the Cv value of expansion valve 5 in FIG. 7 (b) is larger than a resolution Rs1 of the Cv value of expansion valve 5 in FIG. 7 (a).

Thus, when it is assumed that the refrigerant that flows into the expansion valve may both be liquid refrigerant and wet steam, the difference between the maximum value and the minimum value of the Cv value is large, and therefore, the resolution of the Cv value of the expansion valve is large. Namely, the controllability for the expansion valve is deteriorated to increase the difference between the actual refrigerant flow rate and a desired refrigerant flow rate. Since the refrigerant flow rate can be regulated to regulate the capacity of the refrigeration cycle apparatus, deterioration of the controllability for the expansion valve results in deterioration of the controllability for the refrigeration cycle apparatus.

In view of the above, refrigerant in air conditioner 100 that flows into expansion valve 5A and that flows into expansion valve 5B are cooled by internal heat exchangers 6 and 7, respectively. As a result, the density of refrigerant flowing into expansion valves 5A, 5B can be made higher than the density of refrigerant flowing into expansion valves 5C, 5D in air conditioner 900, and therefore, the resolution of expansion valves 5A, 5B can be made lower than the resolution of expansion valves 5C, 5D. Since the controllability for expansion valves 5A, 5B is improved relative to the controllability for expansion valves 5C, 5D, the controllability for air conditioner 100 can be improved relative to the controllability for air conditioner 900.

FIG. 9 is a P-h diagram showing change of the state of refrigerant circulating through air conditioner 100 in FIG. 1. FIG. 10 is a P-h diagram showing change of the state of refrigerant circulating through air conditioner 100 in FIG. 2. Respective states shown in FIGS. 9 and 10 correspond respectively to the states of refrigerant at nodes N1 to N12 in FIGS. 1 and 2. Curves LC and GC represent a saturated liquid line and a saturated vapor line, respectively. Saturated liquid line LC and saturated vapor line GC connect to each other at a critical point CP.

Refrigerant in the state on saturated liquid line LC and refrigerant in the state with an enthalpy lower than the enthalpy of the state on saturated liquid line LC are liquid refrigerant. The region of liquid refrigerant includes saturated liquid line LC. Refrigerant in the state included in the region between saturated liquid line LC and saturated vapor line GC is wet steam. Refrigerant in the state on saturated vapor line GC and refrigerant in the state with an enthalpy higher than the enthalpy of the state on saturated vapor line GC are gaseous liquid (gas liquid). The region of gas refrigerant includes saturated vapor line GC.

With reference to FIGS. 9 and 1, the process from the state at node N1 to the state at node N2 is an adiabatic compression process through compressor 1. Because there is almost no state change of the refrigerant flowing from compressor 1 to heat exchanger 4, the state at node N3 is almost the same as the state at node N2. The process from the state at node N3 to the state at node N4 is a condensation process through heat exchanger 4 serving as a condenser. The state at node N4 is included in the region of liquid refrigerant. Liquid refrigerant at node N4 flows into expansion valve 5A. The process from the state at node N4 to the state at node N5 is an adiabatic expansion process through expansion valve 5A. The state at node N5 is included in the region of wet steam. During a cooling operation, refrigerant from compressor 1 flows toward heat exchanger 4 without passing through internal heat exchanger 6. In internal heat exchanger 6, there is almost no heat exchange between refrigerants, and therefore, the state at node N6 is almost the same as the state at node N5. In the process from the state at node N6 to the state at node N7, a pressure loss is generated due to extension pipe ep1. The state at node N7 is also included in the region of wet steam, like the state at node N6. Namely, wet steam flows through extension pipe ep1 during the cooling operation.

The process from the state at node N7 to the state at node N8 is a cooling process through internal heat exchanger 7. The state at node N8 is a state shifted from the state at node N7 in the direction in which the enthalpy decreases, and included in the region of liquid refrigerant. Liquid refrigerant in the state at node N8 flows into expansion valve 5B. The process from the state at node N8 to the state at node N9 is an adiabatic expansion process through expansion valve 5B. The process from the state at node N9 to the state at node N10 is an evaporation process through heat exchanger 8 serving as an evaporator. The process from the state at node N10 to the state at node N11 is a heating process through internal heat exchanger 7. In the process from the state at node N11 to the state at node N12, a pressure loss is generated due to extension pipe ep2. Because there is almost no state change of the refrigerant flowing from node N12 toward node N1 through four-way valve 2, the state at node N1 is almost the same as the state at node N12.

With reference to FIGS. 10 and 2, the process from the state at node N1 to the state at node N12 is an adiabatic compression process through compressor 1. In the process from the state at node N12 to the state at node N11, a pressure loss is generated due to extension pipe ep2. Because there is almost no state change of the refrigerant flowing from extension pipe ep2 to heat exchanger 8, the state at node N10 is almost the same as the state at node N11. The process from the state at node N10 to the state at node N9 is a condensation process through heat exchanger 8 serving as a condenser. The state at node N9 is included in the region of liquid refrigerant. Liquid refrigerant in the state at node N9 flows into expansion valve 5B. The process from the state at node N9 to the state at node N8 is an adiabatic expansion process through expansion valve 5B. The state at node N8 is included in the region of wet steam. During a heating operation, refrigerant from compressor 1 flows toward heat exchanger 8 without passing through internal heat exchanger 7. In internal heat exchanger 7, there is almost no heat exchange between refrigerants, and therefore, the state at node N7 is almost the same as the state at node N8. In the process from the state at node N7 to the state at node N6, a pressure loss is generated due to extension pipe ep1. The state at node N6 is also included in the region of wet steam, like the state at node N7. Namely, wet steam also flows through extension pipe ep1 during the heating operation.

The process from the state at node N6 to the state at node N5 is a cooling process through internal heat exchanger 6. The state at node N5 is a state shifted from the state at node N6 in the direction in which the enthalpy decreases, and included in the region of liquid refrigerant. Liquid refrigerant in the state at node N5 flows into expansion valve 5A. The process from the state at node N5 to the state at node N4 is an adiabatic expansion process through expansion valve 5A. The process from the state at node N4 to the state at node N3 is an evaporation process through heat exchanger 4 serving as an evaporator. The process from the state at node N3 to the state at node N2 is a heating process through internal heat exchanger 6. Because there is almost no state change of the refrigerant flowing from node N2 toward node N1 through four-way valve 2, the state at node N1 is almost the same as the state at node N2.

Thus, the refrigeration cycle apparatus according to Embodiment 1 can suppress deterioration of the controllability.

Embodiment 2

In connection with Embodiment 2, a case is described in which a receiver capable of storing liquid refrigerant serves as the internal heat exchanger of Embodiment 1. FIG. 11 shows a functional configuration of an air conditioner 200 that is an example of a refrigeration cycle apparatus according to Embodiment 2, together with flow of refrigerant during a cooling operation. The configuration of air conditioner 200 corresponds to the configuration in FIG. 1, except that internal heat exchangers 6 and 7 in FIG. 1 are replaced respectively with a receiver 62 (first receiver) and a receiver 72 (second receiver) that are capable of storing liquid refrigerant. The configuration of air conditioner 200 and that in FIG. 1 are similar to each other except for the above-identified features, and therefore, the description thereof is not herein repeated.

With reference to FIG. 11, wet steam from expansion valve 5A flows into receiver 62. When liquid refrigerant is stored in receiver 62, the liquid refrigerant may flow out of receiver 62. Because the density of liquid refrigerant is higher than the density of wet steam, the amount of the liquid refrigerant stored in receiver 62 decreases with time, and consequently, the refrigerant flowing out of receiver 62 changes form the liquid refrigerant to the wet steam. The liquid refrigerant flows temporarily through extension pipe ep1 and, after the refrigerant flowing out of receiver 62 changes from the liquid refrigerant to the wet steam, the wet steam flows through extension pipe ep1. The refrigerant flowing from extension pipe ep1 into receiver 72 is cooled by refrigerant from heat exchanger 8 serving as an evaporator. As a result, liquid refrigerant flows out of receiver 72 toward expansion valve 5B while excess refrigerant is stored in receiver 72.

FIG. 12 shows the functional configuration of air conditioner 200 in FIG. 11, together with flow of refrigerant during a heating operation. With reference to FIG. 12, wet steam from expansion valve 5B flows into receiver 72. When liquid refrigerant is stored in receiver 72, the liquid refrigerant may flow out of receiver 72. The amount of the liquid refrigerant stored in receiver 72 decreases with time, and consequently, the refrigerant flowing out of receiver 72 changes form the liquid refrigerant to the wet steam. The liquid refrigerant flows temporarily through extension pipe ep1 and, after the refrigerant flowing out of receiver 72 changes from the liquid refrigerant to the wet steam, the wet steam flows through extension pipe ep1. The refrigerant flowing from extension pipe ep1 into receiver 62 is cooled by refrigerant from heat exchanger 4 serving as an evaporator. As a result, liquid refrigerant flows out of receiver 62 toward expansion valve 5A while excess refrigerant is stored in receiver 62.

In connection with Embodiment 2, the above-described refrigeration cycle apparatus includes one outdoor unit and one indoor unit. The refrigeration cycle apparatus according to the embodiments may include a plurality of indoor units and/or a plurality of outdoor units.

Modification of Embodiment 2

The function of each of switches 3 and 9 in FIGS. 1, 2, 11, and 12 is implemented by two check valves. The configuration of the switch of the refrigeration cycle apparatus according to the embodiments is not limited to the configuration including the two check valves. For example, instead of the check valve, an on-off valve controlled by the controller may be used. The function of the switch may also be implemented by a three-way valve.

FIG. 13 shows a functional configuration of an air conditioner 200A that is an example of a refrigeration cycle apparatus according to a modification of Embodiment 2, together with flow of refrigerant during a cooling operation. The configuration of air conditioner 200A corresponds to that in FIG. 11 except that switches 3 and 9 in FIG. 11 are replaced respectively with a three-way valve 3A (first switch) and a three-way valve 9A (second switch) and that controller 10 is replaced with a controller 10A. The configuration in FIG. 13 is similar to that in FIG. 11 except for the above-identified features, and therefore, the description thereof is not herein repeated.

As shown in FIG. 13, three-way valve 3A has a port P31 (first port), a port P32 (second port), and a port P33 (third port). Three-way valve 3A selectively switches the port that communicates with port P31 between ports P32 and P33. Receiver 62 is connected between ports P32 and P33. Port P31 is connected to heat exchanger 4.

Three-way valve 9A has a port P91 (fourth port), a port P92 (fifth port), and a port P93 (sixth port). Three-way valve 9A selectively switches the port that communicates with port P91 between ports P92 and P93. Receiver 72 is connected between ports P92 and P93. Port P91 is connected to heat exchanger 8.

During the cooling operation, port P32 communicates with the discharge port of compressor 1 through four-way valve 2. Controller 10A causes port P31 to communicate with port P32 and causes port P91 to communicate with port P92. Controller 10A controls three-way valve 3A to direct refrigerant from compressor 1 to flow to heat exchanger 4 without flowing through receiver 62. Controller 10A controls three-way valve 9A to direct refrigerant from heat exchanger 8 to flow through receiver 72 to compressor 1.

FIG. 14 shows the functional configuration of air conditioner 200A in FIG. 13, together with flow of refrigerant during a heating operation. As shown in FIG. 14, during the heating operation, port P32 communicates with the suction port of compressor 1 through four-way valve 2. Controller 10A causes port P31 to communicate with port P33 and causes port P91 to communicate with port P93. Controller 10A controls three-way valve 9A to direct refrigerant from compressor 1 to flow to heat exchanger 8 without flowing through receiver 72. Controller 10A controls three-way valve 3A to direct refrigerant from heat exchanger 4 to flow through receiver 62 to compressor 1.

Thus, the refrigeration cycle apparatuses according to Embodiment 2 and the modification can suppress deterioration of the controllability.

The embodiments disclosed herein are intended to be implemented in appropriate combination within the range where they are consistent with each other. It should be construed that the embodiments disclosed herein are given by way of illustration in all respects, not by way of limitation. It is intended that the scope of the present disclosure is defined by claims, not by the description above, and encompasses all modifications equivalent in meaning and scope to the claims.

REFERENCE SIGNS LIST

-   -   1 compressor; 2 four-way valve; 3, 9 switch; 3A, 9A three-way         valve; 4, 8 heat exchanger; 5, 5A-5D expansion valve; 6, 7         internal heat exchanger; 10, 10A controller; 11 circuitry; 12         memory; 13 input/output unit; 31, 32, 91, 92 check valve; 51         main body; 52 valve body; 53 stepper motor; 54, 55 coupling         pipe; 62, 72 receiver; 100, 200, 200A, 900 air conditioner; 110         outdoor unit; 120 indoor unit; 511, 512 valve chamber; 513 valve         seat; 521 leading end; P31-P33, P91-P93 port; ep1, ep2 extension         pipe 

1. A refrigeration cycle apparatus in which a circulation direction of refrigerant is switched between a first circulation direction and a second circulation direction opposite to the first circulation direction, the refrigeration cycle apparatus comprising: a compressor; a first heat exchanger; a second heat exchanger; a third heat exchanger; a fourth heat exchanger; a first expansion valve; and a second expansion valve, the first circulation direction being a circulation direction in order of the compressor, the first heat exchanger, the first expansion valve, the third heat exchanger, the fourth heat exchanger, the second expansion valve and the second heat exchanger, when a circulation direction of the refrigerant is the first circulation direction, the refrigerant from the third heat exchanger exchanging heat with the refrigerant from the second heat exchanger in the fourth heat exchanger, and when a circulation direction of the refrigerant is the second circulation direction, the refrigerant from the fourth heat exchanger exchanging heat with the refrigerant from the first heat exchanger in the third heat exchanger.
 2. The refrigeration cycle apparatus according to claim 1, further comprising a first switch and a second switch, wherein when a circulation direction of the refrigerant is the first circulation direction, the first switch directs the refrigerant from the compressor to flow to the first heat exchanger without flowing through the third heat exchanger, and the second switch directs the refrigerant from the second heat exchanger to flow through the fourth heat exchanger to the compressor, and when a circulation direction of the refrigerant is the second circulation direction, the second switch directs the refrigerant from the compressor to flow to the second heat exchanger without flowing through the fourth heat exchanger, and the first switch directs the refrigerant from the first heat exchanger to flow through the third heat exchanger to the compressor.
 3. The refrigeration cycle apparatus according to claim 2 wherein the first switch comprises a first check valve and a second check valve, the third heat exchanger is connected between an output port of the first check valve and an input port of the second check valve, the output port of the first check valve is connected to the first heat exchanger, the second switch comprises a third check valve and a fourth check valve, the fourth heat exchanger is connected between an input port of the third check valve and an output port of the fourth check valve, an output port of the third check valve is connected to the second heat exchanger and an input port of the fourth check valve, and an input port of the first check valve communicates with a discharge port of the compressor when a circulation direction of the refrigerant is the first circulation direction, and communicates with a suction port of the compressor when a circulation direction of the refrigerant, is the second circulation direction.
 4. The refrigeration cycle apparatus according to claim 2, further comprising a controller configured to control the first switch and the second switch, wherein the first switch comprises a first port, a second port, and a third port, and is configured to selectively switch a port that communicates with the first port, between the second port and the third port, the third heat exchanger is connected between the second port and the third port, the first port is connected to the first heat exchanger, the second switch comprises a fourth port, a fifth port, and a sixth port, and is configured to selectively switch a port that communicates with the fourth port, between the fifth port and the sixth port, the fourth heat exchanger is connected between the fifth port and the sixth port, the fourth port is connected to the second heat exchanger, when a circulation direction of the refrigerant is the first circulation direction, the second port communicates with a discharge port of the compressor, and the controller is configured to cause the first port to communicate with the second port and cause the fourth port to communicate with the fifth port, and when a circulation direction of the refrigerant is the second circulation direction, the second port communicates with a suction port of the compressor, and the controller is configured to cause the first port to communicate with e third port and cause the fourth port to communicate with the sixth port.
 5. The refrigeration cycle apparatus according to claim 1, wherein a state of the refrigerant flowing between the third heat exchanger and the fourth heat exchanger is a gas-liquid two-phase state, when a circulation direction of the refrigerant is the first circulation direction, the refrigerant flowing out of the fourth heat exchanger is in a liquid state, and when a circulation direction of the refrigerant is the second circulation direction, the refrigerant flowing out of the third heat exchanger is in a liquid state.
 6. The refrigeration cycle apparatus according to claim 1, wherein the third heat exchanger comprises a first receiver configured to store the refrigerant, and the fourth heat exchanger comprises a second receiver configured to store the refrigerant.
 7. The refrigeration cycle apparatus according to claim 1, wherein a minimum value and a maximum value of a flow coefficient of the first expansion valve are equal to a minimum value and a maximum value of a flow coefficient of the second expansion valve, respectively, and the maximum value of the flow coefficient of the first expansion value is lower than a maximum value of a flow coefficient required when refrigerant in a gas-liquid two-phase state is assumed to flow into the first expansion valve. 